Calculation of Body Surface Area (BSA) for Blood Volume

figuring of Body Surface Area (BSA) for Blood VolumeCHAPTER 25Calculation of Body Surface Area, Circulating Blood Volume,Requirement of Blood ProductsNamita Mishra, Sudha Rawat, Vishva Nath SharmaBODY SURFACE AREA (BSA)Body surface area (BSA) is the area of the outside surface of the body, expressed in square meters (m2). In physiology and medicine, the body surface area is the measu rubor or calculated surface of tender body. It is lend oneselfd to calculate metabolic, electrolyte, nutritional requirements, drug dosage, and expected pulmonary function measurements. BSA is a measurement used in m whatsoever medical tasks. For many clinical purposes BSA is a interrupt indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass. Nevertheless, there have been several important critiques of the use of BSA in determining the dosage of medications with a narrowtherapeutic indexlike many chemotherapy medications.USES OF THE BSATo gain an appreciat ion of the true required glomerular filtration rate (GFR) renal doance is usually divided by the BSA.To calculate a better approximation of the required cardiac output as for example in children, cardiac index is used.Cardiac output = Cardiac Index / BSAChemotherapy is often dosed according to the perseverings BSA.Glucocorticoid dosing is also expressed in legal injury of BSA for calculating maintenance doses or to compare high dose use with maintenance requirement.CALCULATION OF BSAIt is difficult to actually measure the surface area of the human body so various calculations have been published to arrive at the BSA without direct measurement.The most widely used is the Du Bois formulaBSA = 0.007184 X W0.425 X H0.725A commonly used and simple one is the Mosteller formula0RBSA = ( H X W/ 3600)1/2WhereH = HeightW = weightfor example Patients weight = 65 KgPatients height = 165 cmBSA = (65 X 165)/3600)1/2BSA= 1.72 m2Recently, a weight-based formula was validated in the paediatri c age group that does not include a square root, making it easier to use. It is 4Wkg+7/90+Wkg.AVERAGE VALUESAverage BSA for various weightsWEIGHT (Kg)BSA (m2)1.5 40.13 0.264.1 90.26 0.489.1 140.48 0.5614.1 200.56 0.7120.1 260.71 0.8426.1 340.84 1.034.1 501.0 1.450.1 661.4 1.63Over 66.1Over 1.63EFFECTIVE CIRCULATING muckleBlood stack is the hoi polloi of ancestry (both red stock certificate cells and subscriber line plasma) in the circulatory system of any individual. A typical adult has a blood volume of approximately between 4.7 and 5 liters, with females generally having less blood volume than males. Blood volume (BV) can buoy be calculated given the packed cell volume (HCT the fraction of blood that is red blood cells) and plasma volume (PV)BV = PV/ (1-HCT)Diagnostic technologies are commercially available to measure human blood volume. A recent radio nucleotide study called BVA (Blood Volume Analysis)-100, provides a measure of Red Blood Cells and Plasma with 98% accuracy.BLOOD VOLUME ESTIMATION WEIGHT (kg)BLOOD VOLUME ( ml/kg)New born to 108511 to 208021 to 307531 to 4070Above 4065CIRCULATING VOLUME OF THE CPB CIRCUITPRIMING VOLUME the minimum amount of fluid (hemic or non hemic fluid) used to de- air the complete cardiopulmonary bypass (CPB) rope is called prepare volume or the circulating volume of CPB circuit. Priming of the CPB circuit is an important task for the perfusionist. Generally the main objectives of priming areTo deair the CPB circuitTo check for any leaks in the circuitTo check for any mistake in the assembling of the circuitTo meet the need for the extra volume required to prime the CPB circuit as the unhurrieds blood volume is not sufficient enough to prime the CPB circuit.For achieving sufficient hemodilution.It is a standard practice to use a non blood CPB prime because of the benefits of hemodilution and concerns about blood borne diseases. The total priming volume is determined by the hardware selected for the circuit to be employed. Following are the tables video display the volume required to de-air various oxygenators, arterial filters and tubing.CPB CIRCUIT AND TOTAL PRIMING VOLUME WITH VARIOUS WEIGHT GROUP Weight Group (Kg)Boot size of it(inches)Venous line Size (inches)Arterial line Size (inches)Total Priming Volume (ml)0-41/41/41/44504.1-83/81/41/46008-123/83/81/480012.1-253/83/83/81100251/21/23/81800TUBING SIZE WITH VOLUME (ml/feet)SIZE (inch)VOLUME (ml/feet)3/321.81/82.53/1651/49.653/821.71/238.6SPECIFIC CONSIDERATIONSIn cases where patient is deeply cyanotic the size of the oxygenator and tubing size is selected keeping in mind the requirement of higher degree of hemodilution and higher requirement of arterial blood flows because of the battlefront of large (or major) aorto-pulmonary collaterals (MAPCAs). MAPCAs arise from the aorta or its large branches and supply blood to the pulmonary arteries, because of blockade of the main pulmonary arteries. These MAPCAs steal par t of the cardiac output of the aorta and this heads in reduced systemic perfusion and thus increased pump flows are required during CPB in cyanosed patients with MAPCAs to compensate for this stolen cardiac output.CACULATION OF BLOOD AND BLOOD PRODUCT REQUIREMENTThe packed cell volume (HCT), also known as packed cell volume (PCV) or erythrocyte volume fraction (EVF) is the volume percentage (%) of red blood cells in blood. It is normally about 45% for men and 40% for women. It is considered an integral part of a persons complete blood count along with haemoglobin tautness, white blood cell count, and platelet count. Haemoglobin concentration is reduced as a normal consequence of CPB with hemodilution. Thus the packed cell volume that will result from the hemodilution caused due to priming volume of the CPB circuit should be determined. Several calculations are required to assess hemodilution and blood product requirements. To determine the effects of hemodilution, the volume conc entration formula is used.C1 X Pt BV = C2 X TVon CPBWhere Pt BV = patients blood volume ( patients body weight X blood volume factor)TVon CPB = total volume on CPB (total priming volume + patients total blood volume)C1 = Pre bypass hematocrit of the patient (%)C2 = calculated hemodilutional hematocrit (%)A decision must be made initially regarding the desired hematocrit during cardiopulmonary bypass. Based on the results of the randomized clinical study from Childrens Hospital, Boston ,it seems reasonable to consider a hematocrit of 25% to be the minimal acceptable hematocrit for any cardiopulmonary bypass condition. When the desired hematocrit has been selected the amount of bank blood that must be added to the prime should be calculated. old RBC vol = C3xPt BV + PV Pt RBC volWherePrime RBC vol = volume of blood required in primeC3 = desired HCT on bypassPt BV = patients blood volume ( patients body weight X blood volume factor)PV = total priming volume of the CPB circuit to be us edPt RBC vol = patients blood volume X patients pre bypass hematocritFor examplePatients weight = 5 KgPre bypass hematocrit (C1) = 40%Patients blood volume (Pt BV) = 5 X 85 = 425 ml (85 is blood volume factor for 5 Kg)PV (total priming volume of the CPB circuit to be used) = 600mlTVOn CPB = (600 + 425) = 1025mlCalculated hemodilutional HCT (%) (C2) = C1 X Pt BV / TVon CPB= 40 X 425 / 1025= 16.5 %16.5 is the hematocrit on bypass. If there is a certain desired hematocrit, then to achieve that hematocrit, the amount packed RBCs if needed for the same patient can be calculated as followsC3 (desired HCT) = 30 %Pt BV = 425 mlPV = 600 mlTV On CPB = (Pt BV + PV) = (425 + 600) = 1025 mlPt RBC vol = 425 X 0.40 = 170Prime RBC vol = C3X Pt BV + PV-Pt RBC vol = 0.30 X 1025-170 = 137.5Volume of RBCs needed in prime = 137.5The hematocrit of packed RBCs is 70% thus 137.5/0.70 = 196 ml196 ml of packed RBCs are needed to achieve a hematocrit of 30%.Thus, 196 ml of the clear prime fluid is removed fro m the priming volume to work out for the added packed RBCs. Therefore the calculation of priming volume now has 196 ml of packed RBCs and 404 ml of prime (crystalloid or colloid).In some cyanotic cases where the patients pre bypass hematocrit is more, the blood is diluted to obtain an optimal hematocrit during cardiopulmonary bypass in order to decrease the viscosity of the blood to make better tissue perfusion and to prevent hemolysis. Thus the effect of priming fluid added to dilute the blood can also be calculated asTVon CPB X C4 = TVon CPB 1 X C5WHERETVon CPB = total volume on CPB (total priming volume + patients total blood volume) = 1025mlC4 = Hematocrit (of cyanotic patient) on bypass = 0.60TVon CPB1 = total volume on CPB later on adding 500 ml of priming fluid to the CPB circuit.TVon CPB1 = (1025 + 500) = 1525 mlC5 = the new (affected) HematocritThusC5 = (1025 X 0.60) / 1525 = 0.4040 % is the new hematocrit achieved after adding 500 ml of priming fluid.FIBRINOGENA critica l consideration is plasma factor I dilution. Normal plasma fibrinogen levels are 150-400 mg./dL. The infant/ pediatric patients relative low blood volume with priming requirements of the ECC circuit causes the fibrinogen concentration to be adversely diluted. During CPB, it is desirable to maintain the plasma fibrinogen concentration above 100 mg./dL. in order to prevent impairment of post-CPB hemostasis.Given an example of a 5 Kilogram patient with blood volume of (5 x 85) 425 ml, pre bypass hematocrit of 55%, hematocrit on CPB of 25%, priming volume of 800ml of the circuit to be used for CPB and fibrinogen level of 275 mg/dl. To calculate the effect of priming, patients plasma volume is calculated by following formulaBV = PV/ (1-HCT)PV = (1-HCT) X BVThus PV = (1-0.55) X 425 = 191mlPV = 191mlPatients fibrinogen = 191 X 275 mg/100ml = 525 mgNumber of milligrams required = (425 + 800 ) X (1.00-0.25) = 9.19 dlIf the goal is 100mg/dl, then 919 mg of fibrinogen are needed.Amount of fi brinogen to be added = 919 525 = 394mg.394 mg of fibrinogen must be added to the prime to achieve a goal of 100 mg per dl. FFP usually contains 200 mg of fibrinogen per dl.Thus ml of FPP needed = (394/200) X 100 = 197 ml.Now for the calculation of priming volume the 197ml of the prime fluid (crystalloid or colloid) is replaced by FPP. Thus the clear prime volume becomes 603ml.Suggested readingJianfeng Wang, Eiji Hihara. A unified formula for calculating body surface area of humans and animal. Eur j Appl Physiol.20049213-17Dill DB, Costill DL. Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. J. Appl. Physiol. 1974 37(2)247-248.Tarazi RC .Pulmonary blood volume. Eur Heart J.1985Oct6SupplC43Tarazi RC . Blood volume.. Eur Heart J.19856SupplC41-42